1. Field of the Invention
The present invention relates generally to a color image processing apparatus, for processing a color image, employed for a color image outputting mechanism for expressing a secondary color by superposing a plurality of primary colors. The present invention relates more particularly to a color image processing apparatus for writing source data on the plane of each primary color.
2. Description of the Related Art
A color printer and a color display unit have a plurality of primary colors enough for the apparatus to express in monochrome. Further, secondary colors excluding the primary colors can be expressed by combining those primary colors.
For example, the color printer has at least a yellow (Y), magenta (M) and cyan (C) as the monochromatically-expressible primary colors. Then, red (R), green (G) and blue (B), etc. are expressed with combinations of those primary colors.
The above-described color printer incorporates a bit map memory having a memory plane for every primary color. It is therefore desired that data be written on those memory planes at a high speed.
FIGS. 11 and 11A explanatory diagram showing a prior art.
For instance, the color printer has yellow (Y), magenta (M) and cyan (C) as the monochromatically-printable primary colors. Then, the color printer includes a printing mechanism for each of yellow, magenta and cyan.
Further, correspondingly, the bit map memory has a Y-plane for yellow, a M-plane for magenta and a C-plane for cyan.
Then, an item of bit map data of each plane is outputted to the above printing mechanism for each primary color, thus performing color printing.
The above color printer is capable of performing the printing in colors other than the primary colors in addition to the primary color printing. That is to say, the color printer prints the colors exclusive of the primary colors by combining the plurality of primary colors. For example, green is printed with a combination of yellow and cyan.
Printing the green color entails writing the same source pattern on the Y-plane for yellow and the C-plane for cyan. For instance, as illustrated in FIG. 11, printing a letter "A" in green on a sheet PP involves sequential executions of processes of writing a pattern of the letter "A" on the yellow plane Y-plane and next writing the letter "A" pattern on the cyan plane C-plane.
Furthermore, as illustrated in FIGS. 11 and 11A, printing the above letter "A" in green needs to erase the letter "A" pattern out of the magenta plane M-plane if a background BG is written on the magenta plane M-plane.
Thus, when printing the secondary color other than the primary colors, the conventional writing process to the color bit map memory involves writing sequentially the source data on the combined color planes. Hence, there arises a necessity for a writing time corresponding to the number of planes for expressing the secondary colors, and this leads to such a problem that the high-speed writing can not be effected.
Further, if something is written on a plane of a primary color other than the combined primary colors, a problem is that a process of erasing source pattern thereof must be additionally done.